Magneto-Optical Phenomena in Terahertz Systems

Magneto‐optical phenomena in the terahertz (THz) domain exploit the interaction between THz electromagnetic waves and magnetically biased materials to achieve controlled modulation of amplitude, phase and polarisation. Central effects include Faraday rotation, in which the plane of polarisation rotates under an applied magnetic field, and magnetic circular dichroism, whereby left‐ and right‐handed circularly polarised waves experience different absorption. Such nonreciprocal responses are essential for isolators, circulators and modulators in THz communications, imaging and spectroscopy. Recent advances have focused on two principal routes: first, low‐loss semiconductor platforms such as graphene, indium antimonide (InSb) or rare‐earth garnets, which combine high carrier mobility with strong cyclotron resonances; second, metamaterial and metasurface architectures that amplify magneto‐optical coupling via plasmonic or cavity resonances. These hybrid systems enable ultra‐compact nonreciprocal devices, spin‐selective beam steering and tunable filter functions at room temperature and under modest magnetic fields. The convergence of material science, nanofabrication and THz photonic design now promises integrated circuits offering dynamic isolation, high‐contrast modulation and enhanced sensing based on magneto‐optical effects across 0.1–3 THz.

Research from Nature Portfolio

High‐confinement THz plasmonic cavities have been realised in doped semiconductor crystals, demonstrating record‐small mode volumes down to 10^–8λ_0^3 and efficient tuning of resonant frequencies through temperature control. These ultrasmall cavities reveal nonlocal plasmonic limits and open pathways to ultrastrong light–matter coupling in the THz regime. Complementing this, on-chip isolators based on magneto-optical resonators have achieved unidirectional transmission with isolation ratios exceeding 50 dB and insertion losses below 8 dB near 0.45 THz. Thermal tuning and periodic resonances permit operation over a 90 GHz span, illustrating the feasibility of integrated nonreciprocal components for THz sensing and communications. Seminal work on graphene under magnetic bias has further established electrostatic control of Faraday rotation and dichroism, enabling inversion of magneto-optical signals without varying the applied magnetic field and highlighting the potential of two-dimensional materials for compact THz isolators and modulators.

Magneto-Optical Phenomena in Terahertz Systems publication trend

The graph below shows the total number of articles in magneto-optical phenomena in terahertz systems across all publications each year (not limited to Nature Index journals).

Technical terms

Faraday rotation: Rotation of the plane of polarisation of linearly polarised light as it propagates through a magnetised medium.

Magnetic circular dichroism: Differential absorption of left‐ versus right‐handed circularly polarised waves under a magnetic field.

Nonreciprocity: Phenomenon in which the transmission of electromagnetic waves differs between forward and backward directions.

Plasmon–polariton: Hybrid excitation arising from coupling between electromagnetic waves and charge‐density oscillations at a material interface.

Metasurface: Planar array of subwavelength resonators engineered to control amplitude, phase or polarisation of transmitted or reflected waves.

References

1. Ultrasmall and tunable TeraHertz surface plasmon cavities at the ultimate plasmonic limit. Nature Communications (2023).
2. Terahertz magneto-optical metadevice for active spin-selective beam steering and energy distribution with nonreciprocal isolation. Optica (2023).
3. Electrically controlled terahertz magneto-optical phenomena in continuous and patterned graphene. Nature Communications (2017).
4. Magneto-optical properties of InSb for terahertz applications. AIP Advances (2016).
5. On-chip terahertz isolator with ultrahigh isolation ratios. Nature Communications (2021).